Remove usages of WebContents::GetRenderViewHost().

This CL was uploaded by git cl split.

R=bsep@chromium.org

Bug: 1142671
Change-Id: I7b1fdd8a277ab829520a07e0781a02325d9f43fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500612
Auto-Submit: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Commit-Queue: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821239}

chrome/browser/ui/views/frame/browser_view.cc

@@ -2637,7 +2637,9 @@ void BrowserView::OnWindowBeginUserBoundsChange() {
   if (!web_contents)
     return;
   interactive_resize_in_progress_ = true;
-  web_contents->GetRenderViewHost()->NotifyMoveOrResizeStarted();
+  web_contents->GetMainFrame()
+      ->GetRenderViewHost()
+      ->NotifyMoveOrResizeStarted();
 }
 
 void BrowserView::OnWindowEndUserBoundsChange() {